How Hydrovac Trucks Work

A hydrovac truck works by combining two systems:

A high-pressure water system that breaks up soil
A powerful vacuum system that removes the debris

Think of it as a pressure washer and a giant shop vacuum working together. The water does the digging. The vacuum does the cleanup. Neither system alone could do the job efficiently.

Water without vacuum would create a mud pit. Vacuum without water would be too slow because dry soil doesn't flow through hoses well. Together, they create a fast, precise, and safe excavation method.

Understanding how these systems work helps operators spot problems early and helps fleet managers make smarter maintenance decisions. Every component plays a role in keeping the truck productive.

How Do the Water and Vacuum Systems Work Together?

The water system loosens and liquefies soil while the vacuum system simultaneously removes it.

This happens in real time. As the operator sprays pressurized water into the ground, the vacuum hose hovers inches away, sucking up the wet slurry before it can pool or collapse back into the hole.

The water system handles the hard part, breaking the bond between soil particles. Clay, sand, gravel, and packed earth all resist mechanical force, but high-pressure water cuts through them quickly.

The vacuum system handles volume. It moves hundreds of pounds of material per minute from the excavation site into the debris tank. Without powerful suction, operators would need to manually remove spoils, turning a 30-minute job into a half-day project.

Both systems draw power from the truck's diesel engine. Both require regular maintenance to perform correctly. A failure in either system stops the excavation completely.

For a complete overview of what hydrovac trucks are and why they exist, see our main guide.

How Does the Water System Work?

The water system stores fresh water, pressurizes it through a pump, and delivers it through a handheld wand that the operator aims at the dig location.

Water Tank

The water tank holds the fresh water supply. Capacity ranges from 300 gallons on compact units to 1,500 gallons on full-size trucks. Larger tanks mean longer operating time between refills.

Most tanks are made from aluminum or polyethylene to resist corrosion. Some are insulated to prevent freezing in cold weather. Others include heating elements to keep water liquid during winter operations.

A typical excavation job uses 50 to 150 gallons of water per hour, depending on soil type and dig depth. Sandy soil requires less water than dense clay.

High-Pressure Pump

The water pump pressurizes water from the tank and pushes it through the delivery hose. Most hydrovac pumps produce 2,000 to 3,000 PSI (pounds per square inch). Some heavy-duty units reach 4,000 PSI or higher.

For comparison, a garden hose produces about 40 PSI. A consumer pressure washer produces 1,500 to 2,000 PSI. Hydrovac systems deliver pressure at the high end or above commercial pressure washing equipment.

Pump flow rate matters too. Measured in gallons per minute (GPM), flow rate determines how much water reaches the dig site. Most hydrovac pumps deliver 5 to 10 GPM at full pressure.

The pump connects to the truck's engine through a PTO (power take-off) or runs on its own auxiliary engine. Pump failures stop excavation immediately, making this component critical for uptime.

Water Heater and Boiler Systems

Heated water systems allow excavation in frozen ground. Cold water bounces off frozen soil. Hot water melts frost and ice while cutting through the frozen layer.

Some trucks use inline water heaters that warm water as it flows from tank to wand. Others use boiler systems that pre-heat the entire water supply. Boiler-equipped trucks can produce water temperatures above 180°F.

Winter operations in cold climates require heated water capability. Without it, hydrovac work stops when ground temperatures drop below freezing.

The Wand and Nozzle

The operator holds a wand (also called a lance) connected to a high-pressure hose. The wand is typically 4 to 6 feet long with a trigger or valve to control water flow.

Different nozzle tips attach to the wand end. Each tip produces a different spray pattern:

Pencil jet — Tight, focused stream for cutting through hard soil
Fan spray — Wider pattern for general excavation
Rotating nozzle — Spins to cover more area quickly

Operators switch nozzles based on soil conditions and job requirements. The right nozzle choice affects digging speed and water consumption.

Pressure and Flow Controls

Operators adjust water pressure and flow for different conditions. Hard clay needs maximum pressure. Loose sand needs less pressure but more volume.

Controls are typically located at the operator's station near the dig area. Some systems offer variable pressure settings. Others provide preset options for different soil types.

Proper adjustment prevents wasting water on easy soil and ensures enough cutting power for difficult conditions.

How Does the Vacuum System Work?

The vacuum system creates suction that pulls debris from the excavation through a hose and into the debris tank.

Positive Displacement Blowers

The heart of the vacuum system is the positive displacement (PD) blower. This machine moves air at extremely high volumes to create suction.

A PD blower works by trapping air between rotating lobes and pushing it through the system. As air gets pushed out one side, low pressure forms on the intake side. That low pressure is the suction that pulls debris through the hose.

PD blowers are measured by airflow capacity in CFM (cubic feet per minute). A typical hydrovac blower moves 3,000 to 6,000 CFM. Larger units move even more.

Higher CFM means faster debris removal. But bigger blowers require more engine power and fuel. Truck manufacturers balance blower size against chassis capacity and fuel efficiency.

Vacuum Hose

The vacuum hose carries debris from the dig site to the tank. Most hoses are 6 to 8 inches in diameter. Larger diameter means more material can flow through.

Hose material must resist abrasion from rocks, gravel, and debris. Most hoses use reinforced rubber or polyurethane construction. Even with tough materials, hoses wear out and need regular replacement.

Hose length affects suction power. Longer hoses create more friction, reducing effective vacuum at the pickup point. Most operations keep hose runs under 30 feet when possible.

The Boom System

The boom holds and positions the vacuum hose. It extends from the truck body to reach the excavation site, eliminating the need to park directly over the dig location.

Most booms extend 10 to 25 feet. They rotate 270 to 360 degrees to cover a wide working area from a single truck position.

Hydraulic cylinders raise, lower, and extend the boom. A rotation motor spins it left and right. The operator controls these movements from a control station on the ground or from a wireless remote.

Boom failures are common maintenance issues. Hydraulic seals wear out, rotation motors fail, and control systems malfunction. For pump, blower, and boom repair, experienced technicians diagnose these problems quickly.

How Does the Debris Tank Work?

The debris tank stores excavated material until the truck can dump it at an approved disposal site.

Capacity

Debris tank capacity ranges from 6 cubic yards on small units to 15 cubic yards or more on large trucks. One cubic yard of wet soil weighs approximately 2,000 to 2,500 pounds.

A 12-yard tank at full capacity holds roughly 25,000 to 30,000 pounds of debris. This weight affects truck handling, fuel consumption, and road legality. Many states limit gross vehicle weight, which restricts how full tanks can get before dumping.

Tank Construction

Most debris tanks use heavy-gauge steel construction to handle abrasive slurry and resist corrosion. Interior coatings protect against rust. External reinforcement handles the stress of loading and transport.

Baffles inside the tank prevent slurry from sloshing during transport. Shifting loads affect truck stability, especially during turns and braking.

Dumping Systems

Trucks empty debris tanks using dump doors, full-tilt systems, or a combination.

Dump doors open at the rear of the tank, allowing gravity to pull debris out. The tank may tilt slightly to assist flow.

Full-tilt systems raise the entire tank to steep angles (50 to 70 degrees), dumping all contents quickly. This approach empties tanks more completely but requires heavy hydraulic systems.

Some tanks include pressurization systems that use air pressure to push debris out. This helps with sticky materials that don't flow well under gravity alone.

Why Tank Design Matters

Different materials behave differently in debris tanks. Sandy slurry flows easily and dumps cleanly. Clay-heavy slurry sticks to tank walls and resists dumping.

Tanks designed for one material type may perform poorly with others. Fleet managers in regions with heavy clay soils often specify tanks with steeper tilt angles and interior coatings that resist sticking.

What Is the Step-by-Step Digging Process?

The digging process follows a consistent sequence: position the truck, extend the boom, spray water to loosen soil, vacuum the debris, and repeat until the target depth is reached.

Step 1: Position the Truck

The operator parks the truck as close to the dig location as access allows. Outriggers or stabilizers deploy to level the truck and prevent movement during operation.

Step 2: Locate Utilities

Before any digging begins, the operator confirms 811 utility markings. Colored flags and paint indicate approximate locations of buried gas, electric, water, and telecom lines. The hydrovac will expose these utilities safely for visual confirmation.

Step 3: Extend the Boom

The operator uses controls to extend and position the boom over the dig site. The vacuum hose end hovers near ground level, ready to collect debris.

Step 4: Begin Water Cutting

The operator sprays pressurized water at the ground surface. The stream cuts into soil, turning it into wet slurry. The operator works systematically, cutting a small area at a time.

Step 5: Vacuum Debris

As slurry forms, the vacuum hose picks it up. The operator positions the hose close to the water stream, capturing debris immediately. Slurry travels through the hose and boom into the debris tank.

Step 6: Work in Layers

Excavation proceeds layer by layer. The operator cuts a few inches deep, vacuums the debris, then repeats. This controlled approach prevents undermining or collapse.

Step 7: Expose Utilities

When buried utilities appear, the operator reduces water pressure and works carefully around them. The goal is to expose the utility completely without making contact.

Step 8: Complete the Excavation

The operator continues until reaching target depth or fully exposing the buried infrastructure. Workers can then inspect, repair, or install new components safely.

How Does the Truck's Engine Power Everything?

The diesel engine powers both the truck drivetrain and all excavation equipment through a power take-off (PTO) system.

The Engine

Most hydrovac trucks use diesel engines ranging from 300 to 500+ horsepower. Common engine brands include Cummins, Caterpillar (CAT), Detroit Diesel, PACCAR, and Mack/Volvo.

The engine must produce enough power to drive the truck fully loaded while also running the water pump, vacuum blower, and hydraulic systems simultaneously. Underpowered engines bog down during heavy excavation.

For diesel engine repair on hydrovac trucks, technicians need experience with both the engine itself and how it integrates with auxiliary systems.

Power Take-Off (PTO)

The PTO transfers engine power to auxiliary equipment. It connects to the transmission and drives hydraulic pumps that power the water system, vacuum blower, and boom hydraulics.

When the PTO engages, engine RPM typically increases to provide adequate power. A PTO failure disables all excavation functions even if the engine runs perfectly.

Hydraulic Systems

Hydraulic pumps driven by the PTO create pressure that operates the boom, tank tilt, and other moving components. Hydraulic fluid flows through hoses and cylinders to produce motion.

Hydraulic system failures are among the most common hydrovac breakdowns. Hoses rupture, seals leak, and pumps wear out. Regular inspection prevents unexpected failures.

Why Engine Reliability Matters

Every system on a hydrovac truck depends on the engine. If the engine fails, nothing works. The truck can't drive. The water pump stops. The vacuum blower shuts down. The boom won't move.

Engine problems on a job site mean immediate downtime. The truck must be repaired on location or towed to a shop. Either option costs time and money.

How Do Hydrovac Trucks Operate in Cold Weather?

Hydrovac trucks operate in freezing conditions by using heated water to cut through frozen ground and by protecting water systems from freezing.

Heated Water for Frozen Soil

Standard cold water cannot penetrate frozen ground. The water simply runs off or freezes on contact. Heated water melts frost and ice while cutting into the frozen layer.

Truck-mounted boilers or inline heaters warm water to 140°F to 180°F or higher. Hot water excavation works effectively even when ground temperatures are well below freezing.

Freeze Protection

Water tanks, pumps, and hoses must stay above freezing to function. Insulated tanks slow heat loss. Recirculation systems keep water moving to prevent freezing in lines.

Operators in cold climates drain water systems before overnight parking or keep trucks in heated garages. Frozen pumps and burst hoses are expensive to repair.

Winter Challenges

Cold weather creates additional challenges beyond frozen ground. Diesel engines are harder to start. Hydraulic fluid thickens and flows slowly. Operators face harsh working conditions.

Proper winterization and maintenance preparation make cold-weather operation possible. Neglecting winter prep leads to breakdowns when temperatures drop.

How Do Operators Control the Truck?

Operators control hydrovac trucks using ground-level control stations, wireless remotes, and in-cab controls.

Ground-Level Controls

A control panel mounted on the truck body lets operators manage excavation functions while standing at the dig site. Typical controls include boom movement, vacuum on/off, water pressure adjustment, and engine throttle.

Wireless Remote Controls

Many modern trucks offer wireless remotes that let operators control the boom and other functions from a distance. This improves visibility and lets operators position themselves for the best view of the excavation.

In-Cab Controls

The driver's cab contains standard truck controls plus switches for PTO engagement, outrigger deployment, and system monitoring. Operators set up these functions before leaving the cab to begin excavation.

Safety Interlocks

Safety systems prevent dangerous operations. Interlocks may prevent boom movement unless outriggers are deployed, or stop the vacuum blower if tank pressure exceeds safe limits. Emergency stop buttons allow immediate shutdown.

What Happens When a System Fails?

Any component failure stops productive excavation.

Water pump failure means no cutting power. Blower failure means no suction. Boom failure means no reach. Engine failure means nothing works at all.

Hydrovac trucks combine multiple complex systems that must all function together. A single broken hose, worn seal, or failed sensor can shut down an entire operation.

This is why preventive maintenance matters. Regular inspection catches problems before they cause job-site breakdowns. Worn parts get replaced during scheduled service instead of emergency repairs.

For hydrovac truck parts and components, understanding what each system does helps identify problems early.

When breakdowns happen, fast repair gets trucks back to work. Experienced technicians who understand both diesel mechanics and vacuum excavation systems diagnose problems quickly and fix them correctly the first time.